1. Field of the Invention
The present invention is broadly concerned with expanded, cellular, starch-based extruded products which have compressibility and resiliency properties making them eminently suited for use as packaging fillers or the like, e.g., the well-known "peanuts" used as loose fill packing, or molded packaging components commonly used for protecting electronic components or the like during shipping. More particularly, it is concerned with such extruded products which are improved by provision of a polyalkylene glycol or derivative thereof, and/or a minor amount of a particulate bubble-nucleating agent such as silicon dioxide. Use of these additives gives extrudates having excellent physical properties and desirable uniform, small cells throughout the structure thereof.
2. Description of the Prior Art
Preformed, cellular, high volume, low weight packaging materials formed of polystyrene or similar synthetic resins have for many years been a staple article of commerce. Such products have been produced in a bewildering array of shapes and sizes, depending upon the packaging application in view. While such materials have proven effective for their intended purpose, they are objectionable from an environmental standpoint, in that they persist in the environment for long periods of time. This is especially troublesome because of the large volumes of the products, and the consequent fact that they take up considerable space in landfills.
In response to these concerns, it has been suggested in the past to form biodegradable packaging fillers using starch as a starting material. For example, U.S. Pat. Nos. 4,863,655, 5,035,930 and 5,043,196 describe extruded starch-based fillers made from modified (i.e., hydroxypropylated) high amylose corn starch. A drawback of these products is the relatively high cost of the high amylose starch and the added cost of modifying the starting material. Moreover, these starch-based products do not completely match the desirable properties of prior polystyrene packaging fillers.